Tennis legend Monica Seles has won 53 singles titles, nine Grand Slams and $15 million since she joined the pro tour in 1989. But her toughest opponent doesn't carry a racket.

"In many ways, I think my biggest challenge over the years has actually been learning how to manage my migraine headaches," Ms. Seles says. "I started getting migraines as a teenager, back when I first joined the pro tour. Sometimes, right in the middle of a match, I'd develop a pounding, throbbing headache on the left side of my head, and the pain was almost unbearable.

"I suffered for seven or eight years without knowing what was wrong with me. There were times when I had to miss practice and even pull out of tournaments. I spent entire days lying in darkened rooms, struggling with pain and nausea."

Blaming stress and tension, Ms. Seles played on. "But tennis is a really mental game," she says, and it's hard to win with a throbbing head. She began to mull retirement. Then, in 1997, a neurologist correctly diagnosed her headaches as migraines.

"That changed everything," she says. "Once I understood that I was struggling with an illness -- a medical condition no different than rheumatism, let's say -- I could begin to seek treatment that would help me manage my ailment, day in and day out."

New medications

For Ms. Seles, the key turned out to be a new group of migraine medications called triptans, which stop the rapid shrinking and expansion of blood vessels to the brain. This helps turn off the cascade of chemical imbalances that causes headaches, nausea and visual auras.

"Once I was diagnosed and began taking my medication, it was like a cloud lifted," she says.

"I learned how to spot the early signs of an approaching migraine -- such as exaggerated sensitivity to light -- and I learned that if I took my medicine right at the start of an attack, my symptoms would be much less intense."

This isn't the first time she's faced medical problems. After being stabbed by a fan in 1993, Ms. Seles spent two years in rehabilitation.

Migraines often go untreated

Like Monica Seles, 28 million Americans suffer from migraines.

"Unfortunately, however, research shows that half the migraine sufferers in the United States have never been diagnosed by a physician," says Jan Lewis Brandes, M.D., a migraine researcher at the Vanderbilt University School of Medicine. "As a result, most of them don't know they have a chronic illness, or that recent advances in medical treatment can significantly reduce the discomfort that so often interferes with their daily lives."

Usually caused by sudden chemical imbalances, migraines occur when blood vessels that serve the brain rapidly constrict and then expand. The symptoms often include lightheadedness and flickering visual auras, followed by sharp, throbbing pain in one area of the head. Symptoms can also include nausea and even vomiting. About 70 percent of migraine sufferers are female.

"Migraine attacks can last up to 72 hours if left untreated, and they're often disabling," says Dr. Brandes. "But many women make the mistake of blaming their pain on stress or tension or sinus pressure, and they don't realize there are steps they can take to combat the effects of this medical condition."

Doctors can prescribe a variety of medications to treat and even prevent migraines for those who get a lot of them.

"In many cases, it helps to keep a migraine diary in which you list the triggers that often seem to precede your attacks. Once you identify your triggers, such things as lack of sleep, stress, certain foods and also the kinds of hormonal changes that often accompany menstruation in women, you'll be prepared in advance for the onset of a migraine."

Dr. Brandes advises trying to limit attacks by getting enough sleep, eating a healthy diet, exercising regularly and avoiding large doses of caffeine. Keep medications on hand and take them at the first sign of an attack.